Optical materials have long been recognized as valued additions to security threads used in banknotes. These materials allow for a variety of self-authenticating optical effects while rendering the security thread and thus the banknote more resistant to counterfeiting.
By way of example, U.S. Pat. No. 7,333,268 to Steenblik et al. depicts a film material that employs a regular two-dimensional array of non-cylindrical lenses to enlarge micro-images. In one embodiment, the film material or structure comprises (a) one or more optical spacers; (b) a regular periodic planar array of image icons positioned on one surface of the optical spacer; and (c) a regular periodic array of lenses positioned on an opposing surface of the optical spacer. The lenses are described as being polygonal base multi-zonal lenses, lenses providing enlarged fields of view over the width of the associated image icons so that the peripheral edges of the associated image icons do not drop out of view, or aspheric lenses having effective base diameters of less than 50 microns. For currency, document and product security applications requiring total film thicknesses of less than 50 microns, this reference teaches that the effective base diameter of the lens must be less than 50 microns, and that the focal length of the lens must be less than 40 microns. The images projected by this film structure reportedly show a number of visual effects including orthoparallactic movement.
These micro-optic film structures, in the form of security strips or threads, are either mounted on a surface of a security document (e.g., banknote), or are partially embedded within the document, with the film structures being visible in clearly defined windows on a surface of the document.
Synthetically magnified images which transform from one form, shape, size and/or color into a different form, shape, size and/or color as the film structure is either azimuthally rotated or viewed from different viewpoints are described in this reference. One such method for causing one synthetically magnified image to transform into another synthetically magnified image involves an abrupt change from one icon element pattern to another. As best shown in FIGS. 6a-c of this reference, icon element patterns 92 and 94, while separated on either side of a hard boundary 104, are joined together on the boundary line. As a result, transformation occurs abruptly at this boundary line. Another method described in this reference involves a less abrupt change. In this method, a transition zone is used in the icon array where the size and shape of two icons, which are arranged side-by-side under each lens, gradually change (i.e., either gradually evolving into a larger and more advanced form, or gradually reverting to a smaller and less advanced form) as one moves across the array. While the abruptness of the change is softened by the use of a transition zone, the extent to which the smoothness of synthetic image transformations can be improved, as well as the number and complexity of these image transformations is limited where only two intact icons are involved in each transformation and where the transformations do not occur continuously but rather only during a portion of the time in which the film structure is rotated or viewpoints changed. A need therefore exists for a security device that is capable of more seamlessly transforming projected images into one or several different images along its horizontal and/or vertical axis. A need also exists for a security device that is capable of projecting more than one image at any given viewing angle thereby allowing for the formation of complex, integrated images that are more resistant to simulation.
International Patent Application No. PCT/GB2005/001618 to Commander et al. describes a security device that comprises a substrate having an array of microlenses on one side and one or more corresponding arrays of microimages on the other side. The distance between the microlens array and the microimage array(s) is substantially equal to the focal length of the microlenses. The substrate is sufficiently transparent to enable light to pass through the microlenses so as to reach the microimages. Each microimage is defined by an anti-reflection structure (e.g., a moth-eye structure) on the substrate, which is formed by a periodic array of identical structural elements and an at least partially reflecting layer. Microimages are formed by one or both of the anti-reflection structure and the at least partially reflecting layer. Light passing through the substrate and impinging on the microimages is reflected to a different extent than light which does not impinge on the microimages, thereby rendering the microimages visible.
In an effort to mask variations in orientation and magnification across the device that occur during manufacture, this reference teaches introducing deliberate variations in the image array. One such variation involves modifying the individual images within the microimage array so as to effect a slow rotation in the image across the array (see page 35, lines 23 to 31, and FIG. 42, of PCT/GB2005/001618). Another such variation is described only as changing the shape of the images (see page 35, lines 31 to 33, of PCT/GB2005/001618). Means for achieving such a change in the shape of the images is not disclosed.
A general object of the present invention is to address the needs presented by the prior art by providing stitched icons made up of slices (i.e., narrow bands or strips) from one or more icon designs, wherein each slice is spaced slightly apart from, abuts (i.e., touches or joins at an edge or border), or slightly overlaps an adjacent slice(s), and by further providing a micro-optic security device which employs one or more planar arrangements of such stitched icons. The inventive security device projects at any given viewing angle one or more synthetically magnified images.
The term “frequency”, as used herein, means the number of slices that are present in a stitched icon. By way of example, a stitched icon that has a frequency of 4 means that the stitched icon contains four (4) interleaved slices, and has a period of ¼, while a stitched icon that has a frequency of 2 means that the stitched icon contains two (2) adjacent slices, and has a period of ½.
The micro-optic security device of the present invention comprises a substrate, one or more planar arrangements of stitched icons on or within a surface of the substrate, and one or more planar arrangements of microlenses disposed substantially parallel to the planar arrangement(s) of stitched icons at a distance sufficient for the microlenses to form synthetically magnified images of the icon design(s) embodied in the stitched icons. The size and period of the icon design(s) embodied in the stitched icons can be (in the x and/or y directions) equal to or larger than the size and period of the microlenses. In other words, there may or may not be a one-to-one correlation between the icon design(s) embodied in the stitched icons and the microlenses. This allows for the synthetic display of icon designs that do not “fit” within the boundaries defined by a single microlens period.
In a first contemplated embodiment, the stitched icons are made up of abutting or slightly overlapping slices. By way of the present invention, it has been discovered that a micro-optic security device which employs one or more planar arrangements of stitched icons made up of at least one slice (e.g., vertical slice) from two or more icon designs (the slices abutting or slightly overlapping adjacent slices) will simultaneously project two or more synthetically magnified images. Such simultaneously projected images may be arranged side-by-side to form, for example, a unique pattern or a legible phrase, or may be linked together to form a single, larger, more detailed image. Moreover, such simultaneously projected images may change to one or more different images as the security device is tilted, or as the viewing angle changes.
In a second contemplated embodiment, the stitched icons are made up of slightly spaced apart slices. By way of the present invention, it has been discovered that a micro-optic security device which employs one or more planar arrangements of stitched icons each made up of slightly spaced apart slices (e.g., vertical slices) from two or more icon designs will successively project two or more synthetically magnified images as the device is tilted or viewed from different viewing angles.
In addition to (or instead of) changing from one form to another as the device is tilted or viewed from different viewing angles, the synthetically magnified image(s) projected by the inventive security device may show a number of other visual effects, such as orthoparallactic movement, appearing to lie on a spatial plane deeper than the thickness of the security device, and/or appearing to lie on a spatial plane above a surface of the security device. For example, a first projected image (image A) may appear to lie on a spatial plane deeper than the thickness of the security device before changing to a second projected image (image B), which appears to lie on a spatial plane above a surface of the security device. Image B may then change to a third projected image (image C), which gives an impression of orthoparallactic movement. When two or more images are simultaneously projected, these images may also appear to rapidly switch or trade places.
As will be described in more detail below, the synthetically magnified images projected by the inventive security device may also be animated images that appear to move in a continuous motion.
In a first preferred embodiment, the inventive security device comprises an elongated substrate having a long axis and a short axis and a planar array of stitched icons positioned on or within a surface of the substrate, the planar array having an axis of symmetry within its plane. The stitched icons, each made up of adjacent or interleaved slices from two or more icon designs, are arranged in a plurality of mutually perpendicular columns and rows, and have a repeat period within the planar array. The icon designs or portions thereof embodied in the slices that make up each stitched icon change or transition (in terms of size, shape and/or position) either down each column or across each row. A corresponding planar array of microlenses, having an axis of symmetry within its plane, is disposed substantially parallel to the planar array of stitched icons with the focal points of at least some of the microlenses being substantially aligned with slices in the stitched icons. The distance between the planar arrays is sufficient for the microlenses to form synthetically magnified images of the transitioning icon designs embodied in the slices. The microlenses have a repeat period within the planar array.
The planar arrangement of stitched icons in this first preferred embodiment allows the synthetically magnified image(s) to smoothly transition from one form to at least one other form and then, optionally, back to the original form, in either the horizontal direction or the vertical direction.
In a more preferred embodiment, the ratio of the repeat period of the stitched icons to the repeat period of the microlenses in at least one direction is substantially equal to 1, and the axis of symmetry of the planar array of stitched icons and the corresponding axis of symmetry of the planar array of microlenses are rotationally misaligned, thereby providing orthoparallactic motion effects for the synthetically magnified images of the transitioning icon designs embodied in the slices. In other words, as the security device is tilted, the magnified image changes or evolves as it moves in a direction of tilt that appears to be perpendicular to the direction anticipated by normal parallax.
The rotational misalignment or small pitch mismatch allows a viewer to observe a different part of the transitioning icon designs in each neighboring lens giving the impression that the gradually evolving magnified image is in a different position. As the viewer's eye moves smoothly across the rotationally misaligned arrays, the magnified image, which is orientated at a 90° angle relative to the stitched icons in the planar array, gradually changes form while giving the impression that it is moving orthoparallactically relative to the surface.
In another more preferred embodiment, the ratio of the repeat period of the stitched icons to the repeat period of the microlenses in at least one direction is greater than 1 and the axis of symmetry of the planar array of stitched icons and the corresponding axis of symmetry of the planar array of microlenses are aligned, thereby providing a floating effect for the synthetically magnified images of the transitioning icon designs. In other words, as the security device is tilted, the magnified image changes or evolves while appearing to lie on a spatial plane above a surface of the security device.
In yet another more preferred embodiment, the ratio of the repeat period of the stitched icons to the repeat period of the microlenses in at least one direction is less than 1 and the axis of symmetry of the planar array of stitched icons and the corresponding axis of symmetry of the planar array of microlenses are aligned, thereby providing a deep-set or sunken effect for the synthetically magnified images of the transitioning icon designs. In other words, as the security device is tilted, the magnified image changes or evolves while appearing to lie on a spatial plane deeper than the thickness of the security device.
In a second preferred embodiment, the stitched icons are again made up of adjacent or interleaved slices from two or more icon designs, but placement or interleaving of the slices is done at an angle. More specifically, the inventive micro-optic security device comprises an elongated substrate having a long axis and a short axis and an angled planar array of similarly angled stitched icons positioned on or within a surface of the substrate, the planar array having an axis of symmetry within its plane. The stitched icons are arranged in a plurality of columns and rows and have a repeat period within the planar array. The icon design or portions thereof embodied in each slice in each stitched icon changes or transitions (in terms of size, shape and/or position) either down each column or across each row. A corresponding planar array of microlenses having an axis of symmetry within its plane is disposed substantially parallel to the planar array of stitched icons at a distance sufficient for the microlenses to form synthetically magnified images of the transitioning icon designs. As noted above, the focal points of at least some of the microlenses are substantially aligned with slices in the stitched icons. The microlenses have a repeat period within the planar array.
The novel planar arrangement of stitched icons in this second preferred embodiment allows the synthetically magnified image(s) to smoothly transition from one form to at least one other form and then, optionally, back to the original form, in both the horizontal direction and the vertical direction.
In a more preferred embodiment, the stitched icons are arranged in a plurality of columns and rows in which the rows are parallel to the short axis, while the columns are at an angle (relative to the long axis) ranging from greater than 0 to less than 90°, the ratio of the repeat period of the stitched icons to the repeat period of the microlenses in at least one direction is substantially equal to 1, and the axis of symmetry of the planar array of stitched icons and the corresponding axis of symmetry of the planar array of microlenses are rotationally misaligned, thereby providing the synthetically magnified images of the transitioning icon designs, which are orientated at a 90° angle relative to the stitched icons in the planar array, with orthoparallactic motion effects.
In another more preferred embodiment, the stitched icons are again arranged in a plurality of columns and rows in which the rows are parallel to the short axis, while the columns are again at an angle (relative to the long axis) ranging from greater than 0 to less than 90°. The ratio of the repeat period of the stitched icons to the repeat period of the microlenses in at least one direction, however, is greater than 1, and the axis of symmetry of the planar array of stitched icons and the corresponding axis of symmetry of the planar array of microlenses are aligned, thereby providing a floating effect to the synthetically magnified images of the transitioning icon designs.
In yet another preferred embodiment, the stitched icons are again arranged in a plurality of columns and rows in which the rows are parallel to the short axis, while the columns are again at an angle (relative to the long axis) ranging from greater than 0 to less than 90°. The ratio of the repeat period of the stitched icons to the repeat period of the microlenses in at least one direction, however, is less than 1, and the axis of symmetry of the planar array of stitched icons and the corresponding axis of symmetry of the planar array of microlenses are aligned, thereby providing a deep-set or sunken effect to the synthetically magnified images of the transitioning icon designs.
The present invention further provides a security document or label having opposing surfaces and comprising at least one micro-optic security device, as defined above, partially embedded in and/or mounted on a surface of the security document or label.
In one contemplated embodiment, the synthetically magnified images generated by the inventive micro-optic security device are coordinated with printed images on the device itself and/or on the security document or label.
Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description and accompanying drawings.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.